Breathing apparatus of the kind of which the present invention is concerned is well known and a variety of different constructions have been proposed and the advantages and disadvantages of such apparatus are discussed in many patent specifications. Among the requirements of a satisfactory apparatus are that it supplies adequate quantities of air when the user takes a deep breath which, testing shows, necessitates the supply of a substantially higher flow rate than normally anticipated. It is desirable to minimise power consumption by the motor driving the fan consistent with the requirements set out above to increase battery life.
It is also highly desirable that the air pressure within the face piece or mask is never allowed to fall below the ambient atmospheric pressure. If this happened air may be drawn into the space within the piece or mask drawing environmental contaminants into that space.
The present invention is directed to providing an alternative form of forced air breathing apparatus that, at least in preferred embodiments, allows these desired ends to be achieved.